International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
(Polygonum persicaria)

PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)

United States, Michigan
Ladysthumb (Polygonum persicaria) is a dicot weed in the Polygonaceae family.  In Michigan this weed first evolved resistance to Group 5 (Legacy C1 C2) herbicides in 2001 and infests Blueberries.   Group 5 (Legacy C1 C2) herbicides are known as PSII inhibitors - Serine 264 Binders (Inhbition of Photosynthesis at PSll - Serine 264 Binders ).  Research has shown that these particular biotypes are resistant to atrazine, and simazine and they may be cross-resistant to other Group 5 (Legacy C1 C2) herbicides.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

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QUIK STATS (last updated May 12, 2003 )

Common NameLadysthumb
SpeciesPolygonum persicaria
GroupPSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
Herbicidesatrazine, and simazine
LocationUnited States, Michigan
Contributors - (Alphabetically)Steven Gower 
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Steven Gower
Mature ladysthumb seedheads were collected from a blueberry field in southwest Michigan suspected to be resistant to triazine herbicides. Herbicide resistance was evaluated using a greenhouse plant bioassay. Ladysthumb plants received a PRE application of simazine at 3.96 and 11.88 lbs. ai/A and a POST application of atrazine at 2 and 6 lbs. ai/A (1 and 3X standard field rate, respectively). Other treatments included sensitive and untreated controls. Ladysthumb completely survived applications of simazine and atrazine (1 and 3X rate) with no observed injury, when compared to sensitive and untreated controls. These results indicate that this particular ladysthumb biotype is highly resistant to triazine herbicides.

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Confirmation Tests

Greenhouse trials comparing a known susceptible Ladysthumb biotype with this Ladysthumb biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetic studies on HRAC Group 5 resistant Ladysthumb have not been reported to the site.  There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature
Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.
Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes.  If you have any information pertaining to the fitness of Group 5 (Legacy C1 C2) resistant Ladysthumb from Michigan please update the database.
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Former Weed Science Diagnostician (Now with Monsanto)
Michigan State University
Diagnostic Services
578 Wilson Rd.
East Lansing, 48824, Michigan
United States
Email Steven Gower


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Michigan have been instrumental in providing you this information. Particular thanks is given to Steven Gower for providing detailed information.
Herbicide Resistant Ladysthumb Globally
(Polygonum persicaria)
Herbicide Resistant Ladysthumb Globally
(Polygonum persicaria)
Drag a column header and drop it here to group by that column
Herbicide Resistant Ladysthumb Globally
(Polygonum persicaria)
#CountryFirstYearSituationActive IngredientsSite of Action
1 Czech RepublicCzech Republic 1989 Railways atrazine, cyanazine, lenacil, prometryne, simazine, and terbutryne 12 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
136Polygonum persicariaLadysthumb82
2 FranceFrance 1980 Corn (maize), and Cropland atrazine 17 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
136Polygonum persicariaLadysthumb467
3 New ZealandNew Zealand 1980 Corn (maize) atrazine 30 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
136Polygonum persicariaLadysthumb157
4 NorwayNorway 2009 Spring Barley, and Wheat tribenuron-methyl 31 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
136Polygonum persicariaLadysthumb10977
5 United States (Michigan) United StatesMichigan2001 Blueberries atrazine, and simazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
136Polygonum persicariaLadysthumb5178
Literature about Similar Cases

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